Various safety systems aiming at improving safety have been used in the automotive field.
In recent years, external recognition sensors for detecting objects around a vehicle that are an example of the safety systems are increasingly mounted. Examples of the external recognition sensors include stereo cameras and millimeter wave radars. Use of such safety systems allows detection of objects around a vehicle to alert the driver or perform cruise control depending on the detected surroundings so as to avoid collision of vehicles. Examples of methods for avoiding such collision include a method of detecting a vehicle in front by a stereo camera, alerting the driver if it is determined that the vehicles will collide on the basis of acquired relative speed and relative position between the vehicles, and applying an automatic brake if it is further detected that collision between the vehicles still cannot be avoided to reduce the impact of collision.
When a stereo camera is used, since an inter-vehicle distance or the like is calculated by using disparity information of the same vehicle captured on images acquired by two imaging means (cameras) thereof, there is a problem that the detectable is short and it is difficult to avoid collision when the relative speed is high. In contrast, since a mono camera detects a vehicle position on an image and can calculate an inter-vehicle distance from width information (number of pixels) on the detected image, an assumed width (1.7 m, for example) of a vehicle, and the characteristics of the camera and since the width of a vehicle on an image is larger than the disparity in general, the mono camera can detect an object such as a vehicle at a distance longer than the stereo camera. With the mono camera, however, there is a problem that error from the actual distance is caused when the assumption of the width of a vehicle for calculating the inter-vehicle distance is different from the actual width. In contrast, with the stereo camera, the inter-vehicle distance can be calculated from the disparity independent of the width of a vehicle, there is an advantage that error from the actual distance is less likely to be caused in a short distance range.
Thus, the distance between vehicles or the like can be calculated by a distance calculation technique for a mono camera by using an image acquired by one imaging means of a stereo camera, the distance is output in a long distance range that cannot be detected by the stereo camera while the distance between vehicles or the like obtained by using the accurate stereo camera at a shorter distance to increase the detection distance and allow collision between vehicles to be avoided even the relative speed between the vehicles is large.
When an error is caused in the inter-vehicle distance calculated by using the mono camera and there is thus a difference from the inter-vehicle distance calculated by using the stereo camera, and if the distance is simply switched between the distance calculated by using the mono camera and the distance calculated by using the stereo camera in performing cruise control or the like on the vehicle by using the distances to control the inter-vehicle distance, there is a problem that the inter-vehicle distance suddenly changes in a stepwise manner, which degrades the control result.
To address such problems, PTLS 1 and 2 disclose systems that switch vehicle information from information acquired by one detecting means to information acquired by another detecting means by taking a predetermined transition period to gradually make the vehicle information data converge.